Identification of a DNA Damage-Induced Alternative Splicing Pathway That Regulates p53 and Cellular Senescence Markers

Cellular responses to DNA damage are critical determinants of cancer development and aging-associated pathogenesis. Here, we identify and characterize a DNA-damage response (DDR) pathway that regulates alternative splicing of numerous gene products, including the human tumor suppressor TP53, and controls DNA damage-induced cellular senescence. In brief, ionizing radiation (IR) inhibits the activity of SMG1, a phosphoinositide-3-kinase-like kinase family member, reducing the binding of SMG1 to a specific region near exon 9 of p53 precursor mRNA and promoting the binding of ribosomal protein L26 (RPL26) to p53 pre-mRNA. RPL26, in turn, is required for the recruitment of the serine/arginine-rich splicing factor SRSF7 to p53 pre-mRNA and generation of alternatively spliced p53 beta RNA. Disruption of this pathway via selective knockout of p53 beta by CRISPR/Cas9 or downregulation of pathway constituents significantly reduces IR-induced senescence markers, and cells lacking p53 beta expression fail to transcriptionally repress negative regulators of cellular senescence and aging. SIGNIFICANCE: We identified a new component of the DDR pathway that regulates alternative splicing of messenger RNAs, including human TP53 mRNA. Modulation of this regulatory pathway affects DNA-damage induction of cellular senescence markers. (C) 2017 AACR.